Silvano de Franceschi

Host institution: French Alternative Energies and Atomic Energy Commission

Laboratory: LETI/INAC/NEEL

Call for Projects: Synergy (PE10)

Project name: QUCUBE – 3D integration technology for silicon spin qubits

Amount: 13.99 M€


Originally conceived to describe the microscopic world of atoms and elementary particles, the theory of quantum mechanics has eventually served to predict macroscopic phenomena, e.g. the electrical and optical properties of semiconductors, resulting a wide range of technological applications that have changed our way of living. Foundational properties like quantum superposition and entanglement, however, have remained essentially unexploited. Their use may allow achieving computational powers inaccessible to classical digital computers, opening unprecedented opportunities. In a quantum computer, the elementary bits of information are encoded onto two-level quantum systems called qubits. Since qubits interact with the uncontrolled degrees of freedom of their environment, the evolution of their quantum states can become quickly unpredictable, leading to a reduced qubit fidelity. In topological quantum computing schemes, e.g. the surface code, the reduced fidelity is compensated by using decoherence-free logical qubits consisting of a large number (~103) of entangled physical qubits. As a result, a useful quantum processor should host at least millions of qubits. Although dauntingly large, this number is still small as compared to the number of transistors in a modern silicon microprocessors. QuCube leverages industrial-level silicon technology to realize a quantum processor containing hundreds of spin qubits confined to a two-dimensional array of electrostatically defined silicon quantum dots. To face the challenge of addressing the qubits individually, we use a three-dimensional architecture purposely designed to accommodate, on separated planes, the charge sensing devices necessary for qubit readout, and the metal gate lines for the electrical control and measurement. The gate lines are operated according to a multiplexing principle, enabling a scalable wiring layout. We shall implement fault-tolerant logical qubits and quantum simulations of complex Hamiltonians.

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